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<div class="moz-cite-prefix">On 3/8/2012 2:05 PM, Matthew Knepley
wrote:<br>
</div>
<blockquote
cite="mid:CAMYG4GnSt1vzVr438q+gwUJpGhW4JnaOgahPP-fQdwO6a3P6Ag@mail.gmail.com"
type="cite">On Fri, Aug 3, 2012 at 4:52 AM, TAY wee-beng <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:zonexo@gmail.com" target="_blank">zonexo@gmail.com</a>></span>
wrote:<br>
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0
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<div class="im">On 3/8/2012 11:10 AM, thomas wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
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Hi,<br>
look at the FAQ<br>
<br>
<a moz-do-not-send="true"
href="http://www.mcs.anl.gov/petsc/documentation/faq.html#slowerparallel"
target="_blank">http://www.mcs.anl.gov/petsc/documentation/faq.html#slowerparallel</a><br>
<br>
"There must be enough work for each process to overweigh
the communication time. We recommend an absolute minimum
of about 10,000 unknowns per process, better is 20,000 or
more."<br>
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<br>
</div>
Hi Thomas,<br>
<br>
Thanks for the info.<br>
<br>
Btw, is there an upper limit? When the unknowns are 100,000 or
more per process, is it better (as in faster) to use more
processes instead (e.g. 20,000 per process)?</blockquote>
<div><br>
</div>
<div>That depends on the machine. The lower limit is the minimum
number of unknowns to cover the latency of network
communication.</div>
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</blockquote>
<br>
Thanks for the info!<br>
<blockquote
cite="mid:CAMYG4GnSt1vzVr438q+gwUJpGhW4JnaOgahPP-fQdwO6a3P6Ag@mail.gmail.com"
type="cite">
<div class="gmail_quote">
<div><br>
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<div> Matt</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0
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<blockquote class="gmail_quote" style="margin:0 0 0
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<br>
Regards<br>
Thomas Huxhorn<br>
<br>
On 08/03/2012 09:03 AM, TAY wee-beng wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi,<br>
<br>
I remembered that in one of the mails, someone
mentions the recommended<br>
unknowns on each processor when doing parallel
solving.<br>
<br>
However, I can't find that mail. Can someone enlighten
me? Also, is this<br>
number problem dependent?<br>
<br>
Btw, I'm using PETSc to solve linear equations using
BCGS.<br>
<br>
Thanks!<br>
<br>
</blockquote>
<br>
</blockquote>
<br>
</div>
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<br>
<br clear="all">
<div><br>
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-- <br>
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to
which their experiments lead.<br>
-- Norbert Wiener<br>
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